1. Field of the Invention
The present invention relates generally to the field of wireless networking, and more specifically to self-optimizing networks for fixed wireless access.
2. Description of the Related Art
Traditional network dimensioning and planning rely on expected peak traffic demand of each geographical zone know as busy hour traffic. Static approaches may be used, prior to actual deployment, to predict the required number of pieces of equipment and their locations to satisfy the traffic demand. Additionally, simplified in-house developed models and sophisticated commercial tools could be used during the multiple network planning phases.
The planning process starts with identifying the number of base stations, their best locations, and configurations to achieve coverage, capacity, and quality of service requirements. In most cases, the service provider is limited to existing or predefined site locations because acquiring new sites is becoming more difficult due to increasing concerns about mobile telephony by both the government and the public, and the finite number of tall buildings in a city. Additionally, cellular towers in rural areas are typically subject to zoning approval by local municipalities. As such, site locations are typically shared by more than one service provider.
Due to the continued need for capacity increase and broadband services, existing sites are forced into hosting more equipment for existing or new technologies to satisfy the demand. However, some of the existing sites are becoming congested and it may not be possible to easily add more equipment without altering existing services or neighbors' networks. Therefore, different planning techniques have emerged to help alleviate the current constraints.
For example, a natural solution to increase the capacity of a cellular system without adding new sites is to implement high-order sectorization in hotspot areas where capacity is needed.
In high-order sectorization, the higher the number of sectors per site the greater the number of handover region, which results in less effective sectorization gain. For example, from all to three and six sectors, the effective sectorization gains are 2.5 and 4.3, respectively. However, handover is not supported for fixed wireless access because subscribers are fixed or slowly moving in a bounded area such as inside of buildings. As such, high-order sectorization gains will be close to ideal, that is, proportional to the number of sectors.
It should be noted that more capacity is needed in dense urban environments when the angular spread of multi-path components is approximately 30 degrees. Transmitting with narrow beams from the basestations will radiate power to adjacent sectors and create interference. As such, it is not recommended to deploy antennas with half-power beamwidth less than 30 degrees for sectors serving subscribers in dense urban environments.
Additionally, each sector needs a downlink preamble, or an equivalent control channel, to facilitate the synchronization of served mobile terminals and the identification of used cell/segment and fast fourier transform (“FFT”) size for orthogonal frequency division multiplexing (“OFDM”) systems such as WiMAX. Measurements are made on the preamble and reported to the basestation for link adaptation purposes such that the modulation and coding scheme is adjusted according to the quality of the wireless channel between the basestation and the subscriber. For a tight frequency reuse ratio, which is normally the case in dense urban environments, a small number of pseudo-noise (“PN”) sequences may cause a serious limitation in finding a subset with the best cross-correlation properties. Further, a fixed WiMAX system has a single preamble sequence used in all the sectors of the network. As such, adjacent sectors cannot overlap and use the same RF frequency channel because subscribers in the overlapping zones will then suffer from co-channel interference and may not be able to synchronize. Some care must be taken for sectors pointing to each other if the sectors have to deploy the same frequency channel; in other words, overlap has to be avoided by tilting the antennas, reducing the basestation transmit power, or by any additional means.
Further, traffic density is time varying and not uniform such that much of the additional equipment may not carry any significant traffic the majority of the time, which dramatically degrades the expected spectrum efficiency of a high-order sectorization system. Even in wireless systems where the subscribers are fixed, traffic unbalance may occur as a result of adding and removing subscribers over time as well as the changing of subscriber service level agreements (“SLA”) affecting required bandwidth. Therefore, there exists a need to change the boundaries of the coverage areas to balance traffic loads and improve overall network performance.
Additionally, RF network planning for cellular wireless systems is complex because many assumption have to be made regarding path loss models, propagation channels, traffic demand, subscribers' density, subscribers' profiles in supporting a variety of services and tariff plans, mobility profile, and indoor v. outdoor subscribers. In order to achieve good predicted results, the assumptions have to be continuously validated by performing drive tests and analyzing huge amounts of data to model subscribers' behaviors, and reflect this learning back into the predictions. As such, RF planning is iterative and continuous because network optimization engineers must take into account recent network changes.
Fixed wireless standards were recently enacted as a broadband alternative to digital subscriber line (“DSL”) and asymmetric digital subscriber lines (“ADSL”). Additionally, there exists commercial equipments in the market that do not follow a particular standard and an operator must purchase basestations and subscriber equipment from the same vendor or run the risk that no one else provides interoperable equipment. One example of the above in a pre-WiMAX system with fixed subscribers is iBurst. Additionally, other fixed wireless systems include IEEE802.16d or IEEE802.16e when the subscriber stations are roof-top mounted or used in constrained mobility scenarios (i.e., inside homes, offices, or the like).
For fixed wireless systems following a standard (such as IEEE802.16d or IEEE802.16e as described above), some commercial planning tools have provided new modules to implement the specific features of the air interfaces (e.g. OFDM and orthogonal frequency division multiple access (“OFDMA”)) and supported the fixed nature of subscribers by allowing for subscriber lists rather than generating subscribers randomly to follow predetermined traffic maps. However, the structure of the planning tools and the adopted methodologies were kept the same for new air interfaces and, unlike mobile cellular systems, most of the complexity is not required.
Despite the availability of the planning tool, many small service providers prefer adhoc and heuristic planning for fixed wireless systems rather than paying for expensive RF tools and performing a multitude of tests to calibrate at least the path loss models and propagation assumptions in order to properly apply the planning tools. The same adhoc method apply to fixed wireless systems that do not follow a particular standard especially if the equipment vendors do not supply RF network planning tools.
In view of the above, there exists a need for simplified RF network planning tools for fixed wireless systems that do not use complicated assumptions and, preferably, rely on actual measured data and equipment performance. The desired RF planning tool would also be used for dimensioning as well as for finer adjustments after install, and, further, could be used as a real-time load balancing apparatus to achieve the best network performance at any given time.